This doesn't mean that you can't achieve this effect in Creators Update. In fact, since Anniversary Update, you have the Backdrop brush to sample the in-app content and blur it.

And finally in Creators Update, you can sample the content behind the app window and then set as background, which looks like the app window is transparent(which is NOT).

How to implement it?

Now I will talk about how to Encapsulate a AcrylicBrush.

First of all, you must ensure your project is targeted at Creators Update SDK(Build 15063).

We first build a CompositionBrushBuilder that helps create CompositionEffectBrush which can be applied as a brush in SpriteVisual. The builder pattern is common in Android since I mainly work on Android app.